The employment of MW to extract organic compounds from particulate matter (PM) resulting from air samples has been mainly used in applications of focalized MW in closed systems, however, the high pressures and temperatures reached in this type of equipment compels the development of very sophisticated and expensive systems to achieve high safety standards. One possibility to simplify and reduce costs is to use MW in open systems. Major problems in these types of applications include an inability achieve a good absorption of electromagnetic energy by the organic solvents, the inability to regulate the electromagnetic power produced by the magnetron that generates the MW, and to limit MW radiation leaks, which can cause injury to those who operate these equipments.
Organic solvents are required for the extraction. Most of the appropriate solvents for this purpose (e.g. hexane, toluene and others) have apolar characteristics which makes them impossible to heat using MW.
In the market, there are two types of equipment for chemical extraction with MW, both of high cost, one pressurized and the other one open. In the open configuration, the device is designed for its employment in the generation of specific chemical reactions (e.g. synthesis), where the high energies obtained by the MW are used. In this way, these devices have a very limited capacity for manipulation of the equipment and glass material of traditional and standard use in a laboratory. Furthermore, the requirements for blocking MW leakage restricts the transition zone of these components from the focalized MW zone to the exterior. This problem necessitates the use of glass material specially designed for this purpose or the restriction of typical chemical procedures, such as reflux.
The trouble with the open configuration of MW equipment is the possibility of excessive MW leaks, which can be controlled by limiting the size and shape of the orifices present in the metallic structures that guide and focus the MW in the direction of the container that holds the sample to be heated and extracted, and in the transition zone of the laboratory glass material from the focalized MW zone to the exterior.
U.S. Pat. No. 6,061,926 (“Controlled energy density microwave-assisted processes”, from May 16, 2000, by: Pare J R Jocelyn, Belanger Jacqueline M R and Punt Monique M.) describes the same principle of heating by absorption of MW, but restricted to small volumes of chemical solvents and transition zones, due to the need of limiting MW radiation leaks. This equipment is designed to carry out specific chemical reactions, such as synthesis of chemical compounds.
Consequently, there is a need for equipment that could address those problems of restriction of heating by MW, rapidity, efficiency, volume, safety and use of standard chemical laboratory material.